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Slags are valuable by-products of iron- and steelmaking processes. Their efficient reutilization and the recuperation of their thermal energy are key for improving the overall efficiency of these processes. With the innovative approach presented in this work, it is possible to recover thermal heat from liquid slags. The process concept consists of a slag tundish and four subsequent heat exchangers. The liquid slag is poured into the slag tundish which homogenizes the slag and guarantees a constant mass flow. The heat exchangers extract thermal energy from the slag and transfer it to water or oil. The first module cools the slag from the tapping temperature of about 1500 °C down to 850 °C. Inside the second module, more thermal energy is gathered from the already solidified slag cooling the slag down to ambient temperature. The captured energy can be used for various processes, such as gas preheating or generation of steam. The solidified slag is volume stable and forms amorphous phases, depending on its basicity. The process was designed, and the concept was tested on lab-scale demonstrators with an overall heat recovery rate of 42%. Some applications of the recovered slag heat are also presented in this work. Graphical Abstract Scheme of the process concept with the three heat exchangers and buffer unit.

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Fluxes are added to steelmaking process to form basic slag and limit refractory lining consumption. Early formation of CaO-and MgO-saturated slag is critical for process productivity. To achieve this, flux must be dissolved in the melt in a limited process time, and the properties of a slag additive influence the fluxing efficiency. The dissolution behavior of samples with different qualities (i.e. raw dolomite, limestone, soft-burnt and hard-burnt quicklime and dolime) was investigated in the pre-melted model BOF and EAF slags at 1673 K and 1723 K. The disc-shaped sample was immersed into the melt and left there until slag solidification was reached. After a holding time between 5 and 20 minutes, the crucible with the sample were quenched with liquid nitrogen. The fused samples were analyzed by SEM method. Based on comparison of slag morphology and concentration changes in the slag, the dissolution behavior of the samples was examined.